Ovarian cancer represents the fifth leading cause of cancer-related death among women. However, the mechanisms of ovarian cancer development and its response to treatment remain to be elucidated. Our preliminary results show that ovarian cancer cells generate higher levels of reactive oxygen species (ROS) through NOX4 overexpression compared to immortalized normal ovary epithelial cells. Knockdown of NOX4 in cancer cells decreased ROS production, as well as expression of HER2, HER3 and ATG14. To test how NOX4 is upregulated in ovarian cancer cells, we find that HIF-1 and p70S6K1 are activated in these cells. It is known that HIF-1 and p70S6K1 are activated by oncogenes, such as PI3K and Ras, and by mutations of tumor suppressors, such as PTEN and p53. Our preliminary results indicate that HIF-1 and p70S6K1 induce NOX4 overexpression. We hypothesize that HIF-1 and p70S6K1 induce NOX4 overexpression, which in turn induces HER2/HER3 co-expression and ATG14 expression through miR-199a/miR-152 suppression, leading to ovarian tumor growth, angiogenesis, and therapeutic resistance. We will use multidisciplinary approaches, including molecular biology, animal models and human cancer tissue analysis, to test our hypothesis through three specific aims. Aim 1 will determine whether HIF-1 and p70S6K1 induce NOX4 expression, which in turn mediates HER2 and HER3 co-expression; whether NOX4 regulates trastuzumab treatment resistance through HER2 and HER3, and regulates radiation treatment resistance through induction of autophagy and ATG14 expression. We will manipulate expression of HIF-1, p70S6K1, NOX4 and other molecules in the cells and define the roles of these molecules in trastuzumab and radiation treatment responses. Aim 2 will determine whether NOX4 induces ovarian tumor growth through HER2 and HER3 co-expression via miR-199a suppression using an orthotopic ovarian tumor model, and determine whether NOX4 affects radiation treatment effect via ATG14 using image-guided radiotherapy. Aim 3 will determine whether NOX4 regulates tumor angiogenesis through HER2, HER3, and miR-199a suppression; and investigate whether levels of NOX4, ROS, HER2, HER3, miR-199a, and miR-152 correlate with advanced ovarian cancer stages and survival. Taken together, these results obtained from this application will establish a novel molecular mechanism of NOX4 signaling in regulating ovarian cancer development and provide proof- of-principle as to how NOX4 regulates radiation and trastuzumab treatment resistance. These results will provide the basis for designing a new therapeutic approach by targeting NOX4, HER2/HER3 co-expression, and/or ATG14 for ovarian cancer therapy. These studies will also provide new biomarker(s) using higher levels of NOX4, ROS, ATG14, and/or HER2/HER3 co-expression to predict advanced ovarian cancer stages, radiation or/and trastuzumab treatment resistance in the future.